Biaxial orientation resulting from biaxial stretching is a common way to achieve mechanical, optical, or transmissive properties in extruded or cast films ranging from potato chip bags to water bottles to nicotine patches. A laboratory grade instrument is used in the development of the production processes for a material, ongoing verification during production, and/or support of material scientists who are developing new materials and products. There are many instrumentation options for studying films; however, the primary data generated directly by these instruments are stress-strain curves.
With laboratory biaxial film stretchers, the film sample is clamped on all four sides with the clamps forming a pantograph mechanism. Thus a uniform strain may be applied on opposite sides as the film is stretched in the pantograph mechanism. The pantograph mechanism may often hold the film sample within an oven where temperature can be increased to a desired point since temperature may be a factor whose impact is being determined by the laboratory experimentation.
Conventional laboratory film stretchers utilize pneumatics to operate clamps of the pantograph mechanism. These pneumatics utilize small tubes that stretch from one clamp to the next so that the pneumatic pressure is communicated across all of the clamps for all four sides of the pantograph mechanism. The use of pneumatics for the clamps presents several issues. The tubes exert measurable forces on the clamps during movement of the stretching process, and this force introduces noise into the stress-strain curves being produced. Furthermore, the pneumatics include O-rings and other items that are made of materials that are affected by environmental factors. For example, the pneumatics employ a very dry nitrogen that degrades the O-rings. Furthermore, high temperatures that may be present within the oven during testing and such materials may break down over relatively short intervals. Failures of parts such as O-rings in the clamping system may result in poor clamping of the film sample and ultimately unreliable test results.